Potteries began making porcelain telegraph insulators in the 1850s and 1860s. However, these early insulators tended to be poor quality and were later replaced with cheaper threaded glas insulators. With the advent of electric power distribution in the 1880s, larger and more reliable insulators were needed to carry high voltages acros power lines. Glas was found to be insufficient and the insulator manufacturers once again reverted to using porcelain which, when properly made, was superior in both insulation quality and strength.
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